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Abstract:

An illumination module includes a color conversion cavity with a first
interior surface having a first wavelength converting material and a
second interior surface having a second wavelength converting material. A
first LED is configured to receive a first current and to emit light that
preferentially illuminates the first interior surface. A second LED is
configured to receive a second current and emit light that preferentially
illuminates the second interior surface. The first current and the second
current are selectable to achieve a range of correlated color temperature
(CCT) of light output by the LED based illumination device.

Claims:

1. An LED based illumination device, comprising: a color conversion
cavity comprising a first surface area including a first wavelength
converting material and a second surface area including a second
wavelength converting material; a first LED configured to receive a first
current, wherein light emitted from the first LED enters the color
conversion cavity and primarily illuminates the first wavelength
converting material, the first wavelength converting material is
physically separated from a light emitting surface of the first LED,
wherein a light emitted from the LED based illumination device based on
the light emitted from the first LED has a first color temperature; a
second LED configured to receive a second current, wherein light emitted
from the second LED enters the color conversion cavity and primarily
illuminates the second wavelength converting material, the second
wavelength converting material is physically separated from a light
emitting surface of the second LED, wherein a light emitted from the LED
based illumination device based on light emission from the second LED has
a second color temperature that is different than the first color
temperature; wherein the first current and the second current are
selectable to achieve a range of correlated color temperature (CCT) of
light output by the LED based illumination device; and an output window
over an output port of the color conversion cavity, the output window
comprising at least one of the first wavelength converting material and
the second wavelength converting material, wherein the color conversion
cavity is configured to mix a first light emitted from the first LED and
converted by the first wavelength converting material with a second light
emitted from the second LED and converted by the second wavelength
converting material to produce a combined light that is emitted through
the output window.

2. The LED based illumination device of claim 1, further comprising: a
third LED configured to receive a third current, wherein light emitted
from the third LED enters the color conversion cavity and primarily
illuminates a third wavelength converting material, the third wavelength
converting material is physically separated from a light emitting surface
of the third LED, wherein a light emitted from the LED based illumination
device based on the light emitted from the third LED has a third color
temperature that is different than the first color temperature and the
second color temperature.

3. The LED based illumination device of claim 1, wherein the second LED
and the second wavelength converting material are configured to produce a
color point of the light emitted from the LED based illumination device
that is within a degree of departure Δxy of 0.010 from a target
color point in a CIE 1931 xy diagram when the second current is supplied
to the second LED and the first current is substantially zero.

4. The LED based illumination device of claim 1, wherein the first
wavelength converting material and the second wavelength converting
material are included as part of a transmissive layer physically
separated from and disposed above the first LED and the second LED.

5. The LED based illumination device of claim 1, wherein the first LED
and the second LED each emit light with a peak emission wavelength within
five nanometers of each other.

6. The LED based illumination device of claim 2, wherein the first,
second, and third LEDs each emit light with a peak emission wavelength
within five nanometers of each other.

7. The LED based illumination device of claim 2, wherein the first LED
and the first wavelength converting material are configured to produce
light that is emitted from the LED based illumination device with a color
point below a Planckian locus in CIE 1931 color space, and wherein the
third LED and the third wavelength converting material are configured to
produce light that is emitted from the LED based illumination device with
a color point above the Planckian locus in the CIE 1931 color space.

8. The LED based illumination device of claim 1, wherein more than fifty
percent of light emitted from the first LED is directed to the first
surface area, and wherein more than fifty percent of light emitted from
the second LED is directed to the second surface area.

9. An LED based illumination device, comprising: a color conversion
cavity comprising a first surface area including a first wavelength
converting material and a second surface area including a second
wavelength converting material, the color conversion cavity comprising a
first transmissive element having a first surface area including the
first wavelength converting material and a second surface area including
the second wavelength converting material, and a second transmissive
element disposed above and separated from the first transmissive element,
the second transmissive element includes a third wavelength converting
material; a first LED configured to receive a first current, wherein
light emitted from the first LED enters the color conversion cavity and
preferentially primarily illuminates the first wavelength converting
material, the first wavelength converting material is physically
separated from a light emitting surface of the first LED, wherein a light
emitted from the LED based illumination device based on the light emitted
from the first LED has a first color temperature; a second LED configured
to receive a second current, wherein light emitted from the second LED
enters the color conversion cavity and preferentially primarily
illuminates the second wavelength converting material, the second
wavelength converting material is physically separated from a light
emitting surface of the second LED, wherein a light emitted from the LED
based illumination device based on light emission from the second LED has
a second color temperature that is different than the first color
temperature; a third LED configured to receive a third current, wherein
light emitted from the third LED enters the color conversion cavity and
primarily illuminates the third wavelength converting material; wherein
the first current and the second current are selectable to achieve a
range of correlated color temperature (CCT) of light output by the LED
based illumination device.

10. The LED based illumination device of claim 9, wherein the first
transmissive element is disposed above and separated from the first LED
and the second LED.

11. The LED based illumination device of claim 9, wherein the first,
second, and third LEDs each emit light with a peak emission wavelength
within five nanometers of each other.

12. The LED based illumination device of claim 9, wherein a light emitted
from the LED based illumination device based on the light emitted from
the first LED has a color point below a Planckian locus in CIE 1931 color
space, and wherein the light emitted from the LED based illumination
device based on the light emitted from the third LED has a color point
above the Planckian locus in the CIE 1931 color space.

13. An LED based illumination device, comprising: a color conversion
cavity comprising a first surface area including a first wavelength
converting material and a second surface area including a second
wavelength converting material; a first LED configured to receive a first
current, wherein light emitted from the first LED enters the color
conversion cavity and preferentially primarily illuminates the first
wavelength converting material, the first wavelength converting material
is physically separated from a light emitting surface of the first LED,
wherein a light emitted from the LED based illumination device based on
the light emitted from the first LED has a first color temperature; a
second LED configured to receive a second current, wherein light emitted
from the second LED enters the color conversion cavity and preferentially
primarily illuminates the second wavelength converting material, the
second wavelength converting material is physically separated from a
light emitting surface of the second LED, wherein a light emitted from
the LED based illumination device based on light emission from the second
LED has a second color temperature that is different than the first color
temperature; wherein the second LED is mounted to a mounting board at an
oblique angle with respect to the first LED; and wherein the first
current and the second current are selectable to achieve a range of
correlated color temperature (CCT) of light output by the LED based
illumination device.

14. The LED based illumination device of claim 13, wherein the first
surface area is a transmissive output window and the second surface area
is a reflective sidewall.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of U.S. application Ser. No.
13/560,827, filed Jul. 27, 2012, which, in turn, claims priority under 35
USC 119 to U.S. Provisional Application No. 61/514,258, filed Aug. 2,
2011, both of which are incorporated by reference herein in their
entireties.

TECHNICAL FIELD

[0002] The described embodiments relate to illumination modules that
include Light Emitting Diodes (LEDs).

BACKGROUND

[0003] The use of light emitting diodes in general lighting is still
limited due to limitations in light output level or flux generated by the
illumination devices. Illumination devices that use LEDs also typically
suffer from poor color quality characterized by color point instability.
The color point instability varies over time as well as from part to
part. Poor color quality is also characterized by poor color rendering,
which is due to the spectrum produced by the LED light sources having
bands with no or little power. Further, illumination devices that use
LEDs typically have spatial and/or angular variations in the color.
Additionally, illumination devices that use LEDs are expensive due to,
among other things, the necessity of required color control electronics
and/or sensors to maintain the color point of the light source or using
only a small selection of produced LEDs that meet the color and/or flux
requirements for the application.

[0005] An illumination module includes a color conversion cavity with a
first interior surface having a first wavelength converting material and
a second interior surface having a second wavelength converting material.
A first LED is configured to receive a first current and to emit light
that preferentially illuminates the first interior surface. A second LED
is configured to receive a second current and emit light that
preferentially illuminates the second interior surface. The first current
and the second current are selectable to achieve a range of correlated
color temperature (CCT) of light output by the LED based illumination
device.

[0006] Further details and embodiments and techniques are described in the
detailed description below. This summary does not define the invention.
The invention is defined by the claims.

[0008]FIG. 4 illustrates an exploded view of components of the LED based
illumination module depicted in FIG. 1.

[0009] FIGS. 5A and 5B illustrate perspective, cross-sectional views of
the LED based illumination module depicted in FIG. 1.

[0010]FIG. 6 illustrates a plot of correlated color temperature (CCT)
versus relative flux for a halogen light source and a LED based
illumination device in one embodiment.

[0011]FIG. 7 illustrates a plot of simulated relative power fractions
necessary to achieve a range of CCTs for light emitted from an LED based
illumination module.

[0012]FIG. 8 is illustrative of a cross-sectional, side view of an LED
based illumination module in one embodiment.

[0013] FIG. 9 is illustrative of a top view of the LED based illumination
module depicted in FIG. 8.

[0014]FIG. 10 is illustrative of a top view of an LED based illumination
module that is divided into five zones.

[0015]FIG. 11 is illustrative of a cross-section of an LED based
illumination module in another embodiment.

[0016]FIG. 12 is illustrative of a cross-section of an LED based
illumination module in another embodiment.

[0017]FIG. 13 is illustrative of a cross-section of an LED based
illumination module in another embodiment.

[0018]FIG. 14 is illustrative of a cross-section of an LED based
illumination module in another embodiment.

[0019]FIG. 15 is illustrative of a cross-section of an LED based
illumination module in another embodiment.

[0020]FIG. 16 is illustrative of a cross-sectional, side view of an LED
based illumination module in another embodiment.

[0021]FIG. 17 is illustrative of a top view of the LED based illumination
module depicted in FIG. 16.

[0022]FIG. 18 is illustrative of a top view of an LED based illumination
module in another embodiment.

[0023]FIG. 19 is illustrative of a cross-sectional, side view of the LED
based illumination module depicted in FIG. 18.

[0024]FIG. 20 illustrates a plot of xy color coordinates in the 1931 CIE
color space achieved by the embodiment of the LED based illumination
device 100 illustrated in FIGS. 18-19.

DETAILED DESCRIPTION

[0025] Reference will now be made in detail to background examples and
some embodiments of the invention, examples of which are illustrated in
the accompanying drawings.

[0026] FIGS. 1, 2, and 3 illustrate three exemplary luminaires, all
labeled 150. The luminaire illustrated in FIG. 1 includes an illumination
module 100 with a rectangular form factor. The luminaire illustrated in
FIG. 2 includes an illumination module 100A with a circular form factor.
The luminaire illustrated in FIG. 3 includes an illumination module 100A
integrated into a retrofit lamp device. These examples are for
illustrative purposes. Examples of illumination modules of general
polygonal and elliptical shapes may also be contemplated. Luminaire 150
includes illumination module 100, reflector 125, and light fixture 120.
As depicted, light fixture 120 includes a heat sink capability, and
therefore may be sometimes referred to as heat sink 120. However, light
fixture 120 may include other structural and decorative elements (not
shown). Reflector 125 is mounted to illumination module 100 to collimate
or deflect light emitted from illumination module 100. The reflector 125
may be made from a thermally conductive material, such as a material that
includes aluminum or copper and may be thermally coupled to illumination
module 100. Heat flows by conduction through illumination module 100 and
the thermally conductive reflector 125. Heat also flows via thermal
convection over the reflector 125. Reflector 125 may be a compound
parabolic concentrator, where the concentrator is constructed of or
coated with a highly reflecting material. Optical elements, such as a
diffuser or reflector 125 may be removably coupled to illumination module
100, e.g., by means of threads, a clamp, a twist-lock mechanism, or other
appropriate arrangement. As illustrated in FIG. 3, the reflector 125 may
include sidewalls 126 and a window 127 that are optionally coated, e.g.,
with a wavelength converting material, diffusing material or any other
desired material.

[0027] As depicted in FIGS. 1, 2, and 3, illumination module 100 is
mounted to heat sink 120. Heat sink 120 may be made from a thermally
conductive material, such as a material that includes aluminum or copper
and may be thermally coupled to illumination module 100. Heat flows by
conduction through illumination module 100 and the thermally conductive
heat sink 120. Heat also flows via thermal convection over heat sink 120.
Illumination module 100 may be attached to heat sink 120 by way of screw
threads to clamp the illumination module 100 to the heat sink 120. To
facilitate easy removal and replacement of illumination module 100,
illumination module 100 may be removably coupled to heat sink 120, e.g.,
by means of a clamp mechanism, a twist-lock mechanism, or other
appropriate arrangement. Illumination module 100 includes at least one
thermally conductive surface that is thermally coupled to heat sink 120,
e.g., directly or using thermal grease, thermal tape, thermal pads, or
thermal epoxy. For adequate cooling of the LEDs, a thermal contact area
of at least 50 square millimeters, but preferably 100 square millimeters
should be used per one watt of electrical energy flow into the LEDs on
the board. For example, in the case when 20 LEDs are used, a 1000 to 2000
square millimeter heatsink contact area should be used. Using a larger
heat sink 120 may permit the LEDs 102 to be driven at higher power, and
also allows for different heat sink designs. For example, some designs
may exhibit a cooling capacity that is less dependent on the orientation
of the heat sink. In addition, fans or other solutions for forced cooling
may be used to remove the heat from the device. The bottom heat sink may
include an aperture so that electrical connections can be made to the
illumination module 100.

[0028]FIG. 4 illustrates an exploded view of components of LED based
illumination module 100 as depicted in FIG. 1 by way of example. It
should be understood that as defined herein an LED based illumination
module is not an LED, but is an LED light source or fixture or component
part of an LED light source or fixture. For example, an LED based
illumination module may be an LED based replacement lamp such as depicted
in FIG. 3. LED based illumination module 100 includes one or more LED die
or packaged LEDs and a mounting board to which LED die or packaged LEDs
are attached. In one embodiment, the LEDs 102 are packaged LEDs, such as
the Luxeon Rebel manufactured by Philips Lumileds Lighting. Other types
of packaged LEDs may also be used, such as those manufactured by OSRAM
(Oslon package), Luminus Devices (USA), Cree (USA), Nichia (Japan), or
Tridonic (Austria). As defined herein, a packaged LED is an assembly of
one or more LED die that contains electrical connections, such as wire
bond connections or stud bumps, and possibly includes an optical element
and thermal, mechanical, and electrical interfaces. The LED chip
typically has a size about 1 mm by 1 mm by 0.5 mm, but these dimensions
may vary. In some embodiments, the LEDs 102 may include multiple chips.
The multiple chips can emit light of similar or different colors, e.g.,
red, green, and blue. Mounting board 104 is attached to mounting base 101
and secured in position by mounting board retaining ring 103. Together,
mounting board 104 populated by LEDs 102 and mounting board retaining
ring 103 comprise light source sub-assembly 115. Light source
sub-assembly 115 is operable to convert electrical energy into light
using LEDs 102. The light emitted from light source sub-assembly 115 is
directed to light conversion sub-assembly 116 for color mixing and color
conversion. Light conversion sub-assembly 116 includes cavity body 105
and an output port, which is illustrated as, but is not limited to, an
output window 108. Light conversion sub-assembly 116 may include a bottom
reflector 106 and sidewall 107, which may optionally be formed from
inserts. Output window 108, if used as the output port, is fixed to the
top of cavity body 105. In some embodiments, output window 108 may be
fixed to cavity body 105 by an adhesive. To promote heat dissipation from
the output window to cavity body 105, a thermally conductive adhesive is
desirable. The adhesive should reliably withstand the temperature present
at the interface of the output window 108 and cavity body 105.
Furthermore, it is preferable that the adhesive either reflect or
transmit as much incident light as possible, rather than absorbing light
emitted from output window 108. In one example, the combination of heat
tolerance, thermal conductivity, and optical properties of one of several
adhesives manufactured by Dow Corning (USA) (e.g., Dow Corning model
number SE4420, SE4422, SE4486, 1-4173, or SE9210), provides suitable
performance. However, other thermally conductive adhesives may also be
considered.

[0029] Either the interior sidewalls of cavity body 105 or sidewall insert
107, when optionally placed inside cavity body 105, is reflective so that
light from LEDs 102, as well as any wavelength converted light, is
reflected within the cavity 160 until it is transmitted through the
output port, e.g., output window 108 when mounted over light source
sub-assembly 115. Bottom reflector insert 106 may optionally be placed
over mounting board 104. Bottom reflector insert 106 includes holes such
that the light emitting portion of each LED 102 is not blocked by bottom
reflector insert 106. Sidewall insert 107 may optionally be placed inside
cavity body 105 such that the interior surfaces of sidewall insert 107
direct light from the LEDs 102 to the output window when cavity body 105
is mounted over light source sub-assembly 115. Although as depicted, the
interior sidewalls of cavity body 105 are rectangular in shape as viewed
from the top of illumination module 100, other shapes may be contemplated
(e.g., clover shaped or polygonal). In addition, the interior sidewalls
of cavity body 105 may taper or curve outward from mounting board 104 to
output window 108, rather than perpendicular to output window 108 as
depicted.

[0030] Bottom reflector insert 106 and sidewall insert 107 may be highly
reflective so that light reflecting downward in the cavity 160 is
reflected back generally towards the output port, e.g., output window
108. Additionally, inserts 106 and 107 may have a high thermal
conductivity, such that it acts as an additional heat spreader. By way of
example, the inserts 106 and 107 may be made with a highly thermally
conductive material, such as an aluminum based material that is processed
to make the material highly reflective and durable. By way of example, a
material referred to as Miro®, manufactured by Alanod, a German
company, may be used. High reflectivity may be achieved by polishing the
aluminum, or by covering the inside surface of inserts 106 and 107 with
one or more reflective coatings. Inserts 106 and 107 might alternatively
be made from a highly reflective thin material, such as Vikuiti® ESR,
as sold by 3M (USA), Lumirror® E60L manufactured by Toray (Japan), or
microcrystalline polyethylene terephthalate (MCPET) such as that
manufactured by Furukawa Electric Co. Ltd. (Japan). In other examples,
inserts 106 and 107 may be made from a polytetrafluoroethylene PTFE
material. In some examples inserts 106 and 107 may be made from a PTFE
material of one to two millimeters thick, as sold by W.L. Gore (USA) and
Berghof (Germany). In yet other embodiments, inserts 106 and 107 may be
constructed from a PTFE material backed by a thin reflective layer such
as a metallic layer or a non-metallic layer such as ESR, E60L, or MCPET.
Also, highly diffuse reflective coatings can be applied to any of
sidewall insert 107, bottom reflector insert 106, output window 108,
cavity body 105, and mounting board 104. Such coatings may include
titanium dioxide (TiO2), zinc oxide (ZnO), and barium sulfate (BaSO4)
particles, or a combination of these materials.

[0031] FIGS. 5A and 5B illustrate perspective, cross-sectional views of
LED based illumination module 100 as depicted in FIG. 1. In this
embodiment, the sidewall insert 107, output window 108, and bottom
reflector insert 106 disposed on mounting board 104 define a color
conversion cavity 160 (illustrated in FIG. 5A) in the LED based
illumination module 100. A portion of light from the LEDs 102 is
reflected within color conversion cavity 160 until it exits through
output window 108. Reflecting the light within the cavity 160 prior to
exiting the output window 108 has the effect of mixing the light and
providing a more uniform distribution of the light that is emitted from
the LED based illumination module 100. In addition, as light reflects
within the cavity 160 prior to exiting the output window 108, an amount
of light is color converted by interaction with a wavelength converting
material included in the cavity 160.

[0032] As depicted in FIGS. 1-5B, light generated by LEDs 102 is generally
emitted into color conversion cavity 160. However, various embodiments
are introduced herein to preferentially direct light emitted from
specific LEDs 102 to specific interior surfaces of LED based illumination
module 100. In this manner, LED based illumination module 100 includes
preferentially stimulated color converting surfaces. In one aspect, light
emitted by certain LEDs 102 is preferentially directed to an interior
surface of color conversion cavity 160 that includes a first wavelength
converting material and light emitted from certain other LEDs 102 is
preferentially directed to another interior surface of color conversion
cavity 160 that includes a second wavelength converting material. In this
manner effective color conversion may be achieved more efficiently than
by generally flooding the interior surfaces of color conversion cavity
160 with light emitted from LEDs 102.

[0033] LEDs 102 can emit different or the same colors, either by direct
emission or by phosphor conversion, e.g., where phosphor layers are
applied to the LEDs as part of the LED package. The illumination module
100 may use any combination of colored LEDs 102, such as red, green,
blue, amber, or cyan, or the LEDs 102 may all produce the same color
light. Some or all of the LEDs 102 may produce white light. In addition,
the LEDs 102 may emit polarized light or non-polarized light and LED
based illumination module 100 may use any combination of polarized or
non-polarized LEDs. In some embodiments, LEDs 102 emit either blue or UV
light because of the efficiency of LEDs emitting in these wavelength
ranges. The light emitted from the illumination module 100 has a desired
color when LEDs 102 are used in combination with wavelength converting
materials included in color conversion cavity 160. The photo converting
properties of the wavelength converting materials in combination with the
mixing of light within cavity 160 results in a color converted light
output. By tuning the chemical and/or physical (such as thickness and
concentration) properties of the wavelength converting materials and the
geometric properties of the coatings on the interior surfaces of cavity
160, specific color properties of light output by output window 108 may
be specified, e.g., color point, color temperature, and color rendering
index (CRI).

[0034] For purposes of this patent document, a wavelength converting
material is any single chemical compound or mixture of different chemical
compounds that performs a color conversion function, e.g., absorbs an
amount of light of one peak wavelength, and in response, emits an amount
of light at another peak wavelength.

[0035] Portions of cavity 160, such as the bottom reflector insert 106,
sidewall insert 107, cavity body 105, output window 108, and other
components placed inside the cavity (not shown) may be coated with or
include a wavelength converting material.

[0036] FIG. 5B illustrates portions of the sidewall insert 107 coated with
a wavelength converting material. Furthermore, different components of
cavity 160 may be coated with the same or a different wavelength
converting material.

[0038] In one example, the adjustment of color point of the illumination
device may be accomplished by replacing sidewall insert 107 and/or the
output window 108, which similarly may be coated or impregnated with one
or more wavelength converting materials. In one embodiment a red emitting
phosphor such as a europium activated alkaline earth silicon nitride
(e.g., (Sr,Ca)AlSiN3:Eu) covers a portion of sidewall insert 107 and
bottom reflector insert 106 at the bottom of the cavity 160, and a YAG
phosphor covers a portion of the output window 108. In another
embodiment, a red emitting phosphor such as alkaline earth oxy silicon
nitride covers a portion of sidewall insert 107 and bottom reflector
insert 106 at the bottom of the cavity 160, and a blend of a red emitting
alkaline earth oxy silicon nitride and a yellow emitting YAG phosphor
covers a portion of the output window 108.

[0039] In some embodiments, the phosphors are mixed in a suitable solvent
medium with a binder and, optionally, a surfactant and a plasticizer. The
resulting mixture is deposited by any of spraying, screen printing, blade
coating, or other suitable means. By choosing the shape and height of the
sidewalls that define the cavity, and selecting which of the parts in the
cavity will be covered with phosphor or not, and by optimization of the
layer thickness and concentration of the phosphor layer on the surfaces
of light mixing cavity 160, the color point of the light emitted from the
module can be tuned as desired.

[0040] In one example, a single type of wavelength converting material may
be patterned on the sidewall, which may be, e.g., the sidewall insert 107
shown in FIG. 5B. By way of example, a red phosphor may be patterned on
different areas of the sidewall insert 107 and a yellow phosphor may
cover the output window 108. The coverage and/or concentrations of the
phosphors may be varied to produce different color temperatures. It
should be understood that the coverage area of the red and/or the
concentrations of the red and yellow phosphors will need to vary to
produce the desired color temperatures if the light produced by the LEDs
102 varies. The color performance of the LEDs 102, red phosphor on the
sidewall insert 107 and the yellow phosphor on the output window 108 may
be measured before assembly and selected based on performance so that the
assembled pieces produce the desired color temperature.

[0041] In many applications it is desirable to generate white light output
with a correlated color temperature (CCT) less than 3,100 Kelvin. For
example, in many applications, white light with a CCT of 2,700 Kelvin is
desired. Some amount of red emission is generally required to convert
light generated from LEDs emitting in the blue or UV portions of the
spectrum to a white light output with a CCT less than 3,100 Kelvin.
Efforts are being made to blend yellow phosphor with red emitting
phosphors such as CaS:Eu, SrS:Eu, SrGa2S4:Eu, Ba3Si6O12N2:Eu,
(Sr,Ca)AlSiN3:Eu, CaAlSiN3:Eu, CaAlSi(ON)3:Eu, Ba2SiO4:Eu, Sr2SiO4:Eu,
Ca2SiO4:Eu, CaSi2O2N2:Eu, SrSi2O2N2:Eu, BaSi2O2N2:Eu, Sr8Mg(SiO4)4Cl2:Eu,
Li2NbF7:Mn4+, Li3ScF6:Mn4+, La2O2S:Eu3+ and MgO.MgF2.GeO2:Mn4+ to reach
required CCT. However, color consistency of the output light is typically
poor due to the sensitivity of the CCT of the output light to the red
phosphor component in the blend. Poor color distribution is more
noticeable in the case of blended phosphors, particularly in lighting
applications. By coating output window 108 with a phosphor or phosphor
blend that does not include any red emitting phosphor, problems with
color consistency may be avoided. To generate white light output with a
CCT less than 3,100 Kelvin, a red emitting phosphor or phosphor blend is
deposited on any of the sidewalls and bottom reflector of LED based
illumination module 100. The specific red emitting phosphor or phosphor
blend (e.g. peak wavelength emission from 600 nanometers to 700
nanometers) as well as the concentration of the red emitting phosphor or
phosphor blend are selected to generate a white light output with a CCT
less than 3,100 Kelvin. In this manner, an LED based illumination module
may generate white light with a CCT less than 3,100K with an output
window that does not include a red emitting phosphor component.

[0042] It is desirable for an LED based illumination module, to convert a
portion of light emitted from the LEDs (e.g. blue light emitted from LEDs
102) to longer wavelength light in at least one color conversion cavity
160 while minimizing photon loses. Densely packed, thin layers of
phosphor are suitable to efficiently color convert a significant portion
of incident light while minimizing loses associated with reabsorption by
adjacent phosphor particles, total internal reflection (TIR), and Fresnel
effects.

[0043]FIG. 6 illustrates a plot 200 of correlated color temperature (CCT)
versus relative flux for a halogen light source. Relative flux is plotted
as a percentage of the maximum rated power level of the device. For
example, 100% is operation of the light source at it maximum rated power
level, and 50% is operation of the light source at half its maximum rated
power level. Plotline 201 is based on experimental data collected from a
35W halogen lamp. As illustrated, at the maximum rated power level, the
35W halogen lamp light emission was 2900K. As the halogen lamp is dimmed
to lower relative flux levels, the CCT of light output from the halogen
lamp is reduced. For example, at 25% relative flux, the CCT of the light
emitted from the halogen lamp is approximately 2500K. To achieve further
reductions in CCT, the halogen lamp must be dimmed to very low relative
flux levels. For example, to achieve a CCT less than 2100K, the halogen
lamp must be driven to a relative flux level of less than 5%. Although, a
traditional halogen lamp is capable of achieving CCT levels below 2100K,
it is able to do so only by severely reducing the intensity of light
emitted from each lamp. These extremely low intensity levels leave dining
spaces very dark and uncomfortable for patrons.

[0044] A more desirable option is a light source that exhibits a dimming
characteristic similar to the illustration of line 202. Line 202 exhibits
a reduction in CCT as light intensity is reduced to from 100% to 50%
relative flux. At 50% relative flux, a CCT of 1900K is obtained. Further
reductions, in relative flux do not change the CCT significantly. In this
manner, a restaurant operator may adjust the intensity of the light level
in the environment over a broad range (e.g., 0-50% relative flux) to a
desired level without changing the desirable CCT characteristics of the
emitted light. Line 202 is illustrated by way of example. Many other
exemplary color characteristics for dimmable light sources may be
contemplated.

[0045] In some embodiments, LED based illumination device 100 may be
configured to achieve relatively large changes in CCT with relatively
small changes in flux levels (e.g., as illustrated in line 202 from
50-100% relative flux) and also achieve relatively large changes in flux
level with relatively small changes in CCT (e.g., as illustrated in line
202 from 0-50% relative flux).

[0046]FIG. 7 illustrates a plot 210 of simulated relative power fractions
necessary to achieve a range of CCTs for light emitted from an LED based
illumination module 100. The relative power fractions describe the
relative contribution of three different light emitting elements within
LED based illumination module 100: an array of blue emitting LEDs, an
amount of green emitting phosphor (model BG201A manufactured by
Mitsubishi, Japan), and an amount of red emitting phosphor (model BR102D
manufactured by Mitsubishi, Japan). As illustrated in FIG. 7,
contributions from a red emitting element must dominate over both green
and blue emission to achieve a CCT level below 2100K. In addition, blue
emission must be significantly attenuated.

[0047] Changes in CCT over the full operational range of an LED based
illumination device 100 may be achieved by employing LEDs with similar
emission characteristics (e.g., all blue emitting LEDs) that
preferentially illuminate different color converting surfaces. By
controlling the relative flux emitted from different zones of LEDs (by
independently controlling current supplied to LEDs in different zones as
illustrated in FIG. 8), changes in CCT may be achieved. For example,
changes of more than 300 Kelvin, over the full operational range may be
achieved in this manner.

[0048] Changes in CCT over the operational range of an LED based
illumination device 100 may also be achieved by introducing different
LEDs that preferentially illuminate different color converting surfaces.
By controlling the relative flux emitted from different zones of LEDs of
different types (by independently controlling current supplied to LEDs in
different zones as illustrated in FIG. 8), changes in CCT may be
achieved. For example, changes of more than 500K may be achieved in this
manner.

[0049]FIG. 8 is illustrative of a cross-sectional, side view of an LED
based illumination module in one embodiment. As illustrated, LED based
illumination module includes a plurality of LEDs 102A-102D, a sidewall
107 and an output window 108. Sidewall 107 includes a reflective layer
171 and a color converting layer 172. Color converting layer 172 includes
a wavelength converting material (e.g., a red-emitting phosphor
material). Output window 108 includes a transmissive layer 134 and a
color converting layer 135. Color converting layer 135 includes a
wavelength converting material with a different color conversion property
than the wavelength converting material included in sidewall 107 (e.g., a
yellow-emitting phosphor material). Color conversion cavity 160 is formed
by the interior surfaces of the LED based illumination module including
the interior surface of sidewall 107 and the interior surface of output
window 108.

[0050] The LEDs 102A-102D of LED based illumination module emit light
directly into color conversion cavity 160. Light is mixed and color
converted within color conversion cavity 160 and the resulting combined
light 141 is emitted by LED based illumination module.

[0051] A different current source supplies current to LEDs 102 in
different preferential zones. In the example depicted in FIG. 8, current
source 182 supplies current 185 to LEDs 102C and 102D located in
preferential zone 2. Similarly, current source 183 supplies current 184
to LEDs 102A and 102B located in preferential zone 1. By separately
controlling the current supplied to LEDs located in different
preferential zones, the correlated color temperatures (CCT) of combined
light 141 output by LED based illumination module may be adjusted over a
broad range of CCTs. For example, the range of achievable CCTs may exceed
300 Kelvin. In other examples, the range of achievable CCTs may exceed
500 Kelvin. In yet another example, the range of achievable CCTs may
exceed 1,000 Kelvin. In some examples, the achievable CCT may be less
than 2,000 Kelvin.

[0052] In one aspect, LEDs 102 included in LED based illumination module
are located in different zones that preferentially illuminate different
color converting surfaces of color conversion cavity 160. For example, as
illustrated, some LEDs 102A and 102B are located in zone 1. Light emitted
from LEDs 102A and 102B located in zone 1 preferentially illuminates
sidewall 107 because LEDs 102A and 102B are positioned in close proximity
to sidewall 107. In some embodiments, more than fifty percent of the
light output by LEDs 102A and 102B is directed to sidewall 107. In some
other embodiments, more than seventy five percent of the light output by
LEDs 102A and 102B is directed to sidewall 107. In some other
embodiments, more than ninety percent of the light output by LEDs 102A
and 102B is directed to sidewall 107.

[0053] As illustrated, some LEDs 102C and 102D are located in zone 2.
Light emitted from LEDs 102C and 102D in zone 2 is directed toward output
window 108. In some embodiments, more than fifty percent of the light
output by LEDs 102C and 102D is directed to output window 108. In some
other embodiments, more than seventy five percent of the light output by
LEDs 102C and 102D is directed to output window 108. In some other
embodiments, more than ninety percent of the light output by LEDs 102C
and 102D is directed to output window 108.

[0054] In one embodiment, light emitted from LEDs located in preferential
zone 1 is directed to sidewall 107 that may include a red-emitting
phosphor material, whereas light emitted from LEDs located in
preferential zone 2 is directed to output window 108 that may include a
green-emitting phosphor material and a red-emitting phosphor material. By
adjusting the current 184 supplied to LEDs located in zone 1 relative to
the current 185 supplied to LEDs located in zone 2, the amount of red
light relative to green light included in combined light 141 may be
adjusted. In addition, the amount of blue light relative to red light is
also reduced because the a larger amount of the blue light emitted from
LEDs 102 interacts with the red phosphor material of color converting
layer 172 before interacting with the green and red phosphor materials of
color converting layer 135. In this manner, the probability that a blue
photon emitted by LEDs 102 is converted to a red photon is increased as
current 184 is increased relative to current 185. Thus, control of
currents 184 and 185 may be used to tune the CCT of light emitted from
LED based illumination module from a relatively high CCT (e.g.,
approximately 3,000 Kelvin) to a relatively low CCT (e.g., approximately
2,000 Kelvin) in accordance with the proportions indicated in FIG. 7.

[0055] In some embodiments, LEDs 102A and 102B in zone 1 may be selected
with emission properties that interact efficiently with the wavelength
converting material included in sidewall 107. For example, the emission
spectrum of LEDs 102A and 102B in zone 1 and the wavelength converting
material in sidewall 107 may be selected such that the emission spectrum
of the LEDs and the absorption spectrum of the wavelength converting
material are closely matched. This ensures highly efficient color
conversion (e.g., conversion to red light). Similarly, LEDs 102C and 102D
in zone 2 may be selected with emission properties that interact
efficiently with the wavelength converting material included in output
window 108. For example, the emission spectrum of LEDs 102C and 102D in
zone 2 and the wavelength converting material in output window 108 may be
selected such that the emission spectrum of the LEDs and the absorption
spectrum of the wavelength converting material are closely matched. This
ensures highly efficient color conversion (e.g., conversion to red and
green light).

[0056] Furthermore, employing different zones of LEDs that each
preferentially illuminates a different color converting surface minimizes
the occurrence of an inefficient, two-step color conversion process. By
way of example, a photon 138 generated by an LED (e.g., blue, violet,
ultraviolet, etc.) from zone 2 is directed to color converting layer 135.
Photon 138 interacts with a wavelength converting material in color
converting layer 135 and is converted to a Lambertian emission of color
converted light (e.g., green light). By minimizing the content of
red-emitting phosphor in color converting layer 135, the probability is
increased that the back reflected red and green light will be reflected
once again toward the output window 108 without absorption by another
wavelength converting material. Similarly, a photon 137 generated by an
LED (e.g., blue, violet, ultraviolet, etc.) from zone 1 is directed to
color converting layer 172. Photon 137 interacts with a wavelength
converting material in color converting layer 172 and is converted to a
Lambertian emission of color converted light (e.g., red light). By
minimizing the content of green-emitting phosphor in color converting
layer 172, the probability is increased that the back reflected red light
will be reflected once again toward the output window 108 without
reabsorption.

[0057] In another embodiment, LEDs 102 positioned in zone 2 of FIG. 8 are
ultraviolet emitting LEDs, while LEDs 102 positioned in zone 1 of FIG. 8
are blue emitting LEDs. Color converting layer 172 includes any of a
yellow-emitting phosphor and a green-emitting phosphor. Color converting
layer 135 includes a red-emitting phosphor. The yellow and/or green
emitting phosphors included in sidewall 107 are selected to have
narrowband absorption spectra centered near the emission spectrum of the
blue LEDs of zone 1, but far away from the emission spectrum of the
ultraviolet LEDs of zone 2. In this manner, light emitted from LEDs in
zone 2 is preferentially directed to output window 108, and undergoes
conversion to red light. In addition, any amount of light emitted from
the ultraviolet LEDs that illuminates sidewall 107 results in very little
color conversion because of the insensitivity of these phosphors to
ultraviolet light. In this manner, the contribution of light emitted from
LEDs in zone 2 to combined light 141 is almost entirely red light. In
this manner, the amount of red light contribution to combined light 141
can be influenced by current supplied to LEDs in zone 2. Light emitted
from blue LEDs positioned in zone 1 is preferentially directed to
sidewall 107 and results in conversion to green and/or yellow light. In
this manner, the contribution of light emitted from LEDs in zone 1 to
combined light 141 is a combination of blue and yellow and/or green
light. Thus, the amount of blue and yellow and/or green light
contribution to combined light 141 can be influenced by current supplied
to LEDs in zone 1.

[0058] To emulate the desired dimming characteristics illustrated by line
202 of FIG. 6, LEDs in zones 1 and 2 may be independently controlled. For
example, at 2900K, the LEDs in zone 1 may operate at maximum current
levels with no current supplied to LEDs in zone 2. To reduce the color
temperature, the current supplied to LEDs in zone 1 may be reduced while
the current supplied to LEDs in zone 2 may be increased. Since the number
of LEDs in zone 2 is less than the number in zone 1, the total relative
flux of LED based illumination module is reduced. Because LEDs in zone 2
contribute red light to combined light 141, the relative contribution of
red light to combined light 141 increases. As indicated in FIG. 7, this
is necessary to achieve the desired reduction in CCT. At 1900K, the
current supplied to LEDs in zone 1 is reduced to a very low level or zero
and the dominant contribution to combined light comes from LEDs in zone
2. To further reduce the output flux of LED based illumination module,
the current supplied to LEDs in zone 2 is reduced with little or no
change to the current supplied to LEDs in zone 1. In this operating
region, combined light 141 is dominated by light supplied by LEDs in zone
2. For this reason, as the current supplied to LEDs in zone 2 is reduced,
the color temperature remains roughly constant (1900K in this example).

[0059] FIG. 9 is illustrative of a top view of LED based illumination
module depicted in FIG. 8. Section A depicted in FIG. 9 is the
cross-sectional view depicted in FIG. 8. As depicted, in this embodiment,
LED based illumination module is circular in shape as illustrated in the
exemplary configurations depicted in FIG. 2 and FIG. 3. In this
embodiment, LED based illumination module is divided into annular zones
(e.g., zone 1 and zone 2) that include different groups of LEDs 102. As
illustrated, zones 1 and zones 2 are separated and defined by their
relative proximity to sidewall 107. Although, LED based illumination
module, as depicted in FIGS. 8 and 9, is circular in shape, other shapes
may be contemplated. For example, LED based illumination module may be
polygonal in shape. In other embodiments, LED based illumination module
may be any other closed shape (e.g., elliptical, etc.). Similarly, other
shapes may be contemplated for any zones of LED based illumination
module.

[0060] As depicted in FIG. 9, LED based illumination module is divided
into two zones. However, more zones may be contemplated. For example, as
depicted in FIG. 10, LED based illumination module is divided into five
zones. Zones 1-4 subdivide sidewall 107 into a number of distinct color
converting surfaces. In this manner light emitted from LEDs 1021 and 102J
in zone 1 is preferentially directed to color converting surface 221 of
sidewall 107, light emitted from LEDs 102B and 102E in zone 2 is
preferentially directed to color converting surface 220 of sidewall 107,
light emitted from LEDs 102F and 102G in zone 3 is preferentially
directed to color converting surface 223 of sidewall 107, and light
emitted from LEDs 102A and 102H in zone 4 is preferentially directed to
color converting surface 222 of sidewall 107. The five zone configuration
depicted in FIG. 10 is provided by way of example. However, many other
numbers and combinations of zones may be contemplated.

[0061] In one embodiment, color converting surfaces zones 221 and 223 in
zones 1 and 3, respectively may include a densely packed yellow and/or
green emitting phosphor, while color converting surfaces 220 and 222 in
zones 2 and 4, respectively, may include a sparsely packed yellow and/or
green emitting phosphor. In this manner, blue light emitted from LEDs in
zones 1 and 3 may be almost completely converted to yellow and/or green
light, while blue light emitted from LEDs in zones 2 and 4 may only be
partially converted to yellow and/or green light. In this manner, the
amount of blue light contribution to combined light 141 may be controlled
by independently controlling the current supplied to LEDs in zones 1 and
3 and to LEDs in zones 2 and 4. More specifically, if a relatively large
contribution of blue light to combined light 141 is desired, a large
current may be supplied to LEDs in zones 2 and 4, while a current
supplied to LEDs in zones 1 and 3 is minimized. However, if relatively
small contribution of blue light is desired, only a limited current may
be supplied to LEDs in zones 2 and 4, while a large current is supplied
to LEDs in zones 1 and 3. In this manner, the relative contributions of
blue light and yellow and/or green light to combined light 141 may be
independently controlled. This may be useful to tune the light output
generated by LED based illumination module to match a desired dimming
characteristic (e.g., line 202). The aforementioned embodiment is
provided by way of example. Many other combinations of different zones of
independently controlled LEDs preferentially illuminating different color
converting surfaces may be contemplated to a desired dimming
characteristic.

[0062] In some embodiments, the locations of LEDs 102 within LED based
illumination module are selected to achieve uniform light emission
properties of combined light 141. In some embodiments, the location of
LEDs 102 may be symmetric about an axis in the mounting plane of LEDs 102
of LED based illumination module. In some embodiments, the location of
LEDs 102 may be symmetric about an axis perpendicular to the mounting
plane of LEDs 102. Light emitted from some LEDs 102 is preferentially
directed toward an interior surface or a number of interior surfaces and
light emitted from some other LEDs 102 is preferentially directed toward
another interior surface or number of interior surfaces of color
conversion cavity 160. The proximity of LEDs 102 to sidewall 107 may be
selected to promote efficient light extraction from color conversion
cavity 160 and uniform light emission properties of combined light 141.
In such embodiments, light emitted from LEDs 102 closest to sidewall 107
is preferentially directed toward sidewall 107. However, in some
embodiments, light emitted from LEDs close to sidewall 107 may be
directed toward output window 108 to avoid an excessive amount of color
conversion due to interaction with sidewall 107. Conversely, in some
other embodiments, light emitted from LEDs distant from sidewall 107 may
be preferentially directed toward sidewall 107 when additional color
conversion due to interaction with sidewall 107 is necessary.

[0063]FIG. 11 is illustrative of a cross-section of LED based
illumination module in another embodiment. In the illustrated embodiment,
sidewalls 107A are disposed at an oblique angle, α, with respect to
mounting board 104. In this manner, a higher percentage of light emitted
from LEDs in preferential zone 1 (e.g., LEDs 102A and 102B) directly
illuminates sidewall 107A. In some embodiments, more than fifty percent
of the light output by LEDs 102A and 102B is directed to sidewall 107A.
For example, as illustrated in FIG. 11, LEDs in zone 1 (e.g., LED 102A)
are located a distance, D, from sidewall 107A. In addition, sidewall 107A
extends a distance, H, from mounting board 104 to output window 108.
Assuming that LED 102A exhibits an axi-symmetric output beam distribution
and oblique angle, α, is chosen as follows:

α ≦ tan - 1 ( H D ) ( 1 )
##EQU00001##

[0064] then more than fifty percent of the light output by LEDs in zone 1
is directed to sidewall 107A. In some other embodiments, oblique angle,
α, is selected such that more than seventy five percent of the
light output by LEDs in zone 1 is directed to sidewall 107A. In some
other embodiments, oblique angle, cc, is selected such that more than
ninety percent of the light output by LEDs in zone 1 is directed to
sidewall 107A.

[0065]FIG. 12 is illustrative of a cross-section of LED based
illumination module in another embodiment. In the illustrated embodiment,
LEDs 102 located in preferential zone 1 (e.g., LEDs 102A and 102B) are
mounted at an oblique angle, β, with respect to LEDs in preferential
zone 2. In this manner, a higher percentage of light emitted from LEDs in
preferential zone 1 directly illuminates sidewall 107. In the illustrated
embodiment, an angled mounting pad 161 is employed to mount LEDs in
preferential zone 1 at an oblique angle with respect to mounting board
104. In another example (not shown), LEDs in preferential zone 1 may be
mounted to a three dimensional mounting board that includes a mounting
surface(s) for LEDs in preferential zone 1 oriented at an oblique angle
with respect to a mounting surface(s) for LEDs in preferential zone 2. In
yet another example, mounting board 104 may be deformed after being
populated with LEDs 102 such that LEDs in preferential zone 1 are
oriented at an oblique angle with respect to LEDs in preferential zone 2.
In yet another example, LEDs in preferential zone 1 may be mounted to a
separate mounting board. The mounting board including LEDs in
preferential zone 1 may be oriented at an oblique angle with respect to
the mounting board including LEDs in preferential zone 2. Other
embodiments may be contemplated. In some embodiments, oblique angle,
β, is selected such that more than fifty percent of the light output
by LEDs 102A and 102B is directed to sidewall 107. In some other
embodiments, oblique angle, β, is selected such that more than
seventy five percent of the light output by LEDs 102A and 102B is
directed to sidewall 107. In some other embodiments, oblique angle,
β, is selected such that more than ninety percent of the light
output by LEDs 102A and 102B is directed to sidewall 107.

[0066]FIG. 13 is illustrative of a cross-section of LED based
illumination module in another embodiment. In the illustrated embodiment,
a transmissive element 162 is disposed above and separated from LEDs 102A
and 102B. As illustrated, transmissive element 162 is located between LED
102A and output window 108. In some embodiments, transmissive element 162
includes the same wavelength converting material as the material included
with sidewall 107. In the aforementioned embodiment, blue light emitted
from LEDs in preferential zone 1 is preferentially directed to sidewall
107 and interacts with a red phosphor located in color converting layer
172 to generate red light. To enhance the conversion of blue light to red
light, a transmissive element 162 including the red phosphor of color
converting layer 172 may be disposed above any of the LEDs located in
preferential zone 1. In this manner, light emitted from any of the LEDs
located in preferential zone 1 is preferentially directed to transmissive
element 162. In addition, light emitted from transmissive element 162 may
be preferentially directed to sidewall 107 for additional conversion to
red light.

[0067] In some embodiments, a transmissive element 163 including a yellow
and/or green phosphor may also be disposed above any of the LEDs located
in preferential zone 2. In this manner, light emitted from any of the
LEDs located in preferential zone 2 is more likely to undergo color
conversion before exiting LED based illumination module as part of
combined light 141.

[0068] In some other embodiments, transmissive element 162 includes a
different wavelength converting material from the wavelength converting
materials included in sidewall 107 and output window 108. In some
embodiments, a transmissive element 162 may be located above some of the
LEDs in any of preferential zones 1 and 2. In some embodiments,
transmissive element 162 is a dome shaped element disposed over an
individual LED 102. In some other embodiments, transmissive element 162
is a shaped element disposed over a number of LEDs 102 (e.g., a bisected
toroid shape disposed over the LEDs 102 in preferential zone 1 of a
circular shaped LED based illumination module, or a linearly extending
shape disposed over a number of LEDs 102 arranged in a linear pattern).

[0069] In some embodiments, the shape of transmissive element 162 disposed
above LEDs 102 located in preferential zone 1 is different than the shape
of a transmissive element 162 disposed above LEDs 102 located in
preferential zone 2.

[0070] For example, the shape of transmissive element 162 disposed above
LEDs 102 located in preferential zone 1 is selected such that light
emitted from LEDs located in preferential zone 1 preferentially
illuminates sidewall 107. In some embodiments, transmissive element 162
is selected such that more than fifty percent of the light output by LEDs
located in preferential zone 1 is directed to sidewall 107. In some other
embodiments, transmissive element 162 is selected such that more than
seventy five percent of the light output by LEDs located in preferential
zone 1 is directed to sidewall 107. In some other embodiments,
transmissive element 162 is selected such that more than ninety percent
of the light output by LEDs located in preferential zone 1 is directed to
sidewall 107.

[0071] Similarly, any transmissive element disposed above LEDs 102 located
in preferential zone 2 is shaped to preferentially illuminate output
window 108. In some embodiments, transmissive element 163 is selected
such that more than fifty percent of the light output by LEDs located in
preferential zone 2 is directed to output window 108. In some other
embodiments, transmissive element 163 is selected such that more than
seventy five percent of the light output by LEDs located in preferential
zone 2 is directed to output window 108. In some other embodiments,
transmissive element 163 is selected such that more than ninety percent
of the light output by LEDs located in preferential zone 2 is directed to
output window 108.

[0072]FIG. 14 is illustrative of a cross-section of LED based
illumination module in another embodiment. In the illustrated embodiment,
an interior surface 166 extends from mounting board 104 toward output
window 108. In some embodiments, the height, H, of surface 166 is
determined such that at least fifty percent of the light emitted from
LEDs in preferential zone 1 directly illuminates either sidewall 107 or
interior surface 166. In some other embodiments, the height, H, of
interior surface 166 is determined such that at least seventy five
percent of the light emitted from LEDs in preferential zone 1 directly
illuminates either sidewall 107 or interior surface 166. In yet some
other embodiments, the height, H, of interior surface 166 is determined
such that at least ninety percent of the light emitted from LEDs in
preferential zone 1 directly illuminates either sidewall 107 or interior
surface 166.

[0073] In some embodiments, interior surface 166 includes a reflective
surface 167 and a color converting layer 168. In the illustrated
embodiment, color converting layer 168 is located on the side of
reflective surface 167 that faces sidewall 107. In addition, color
converting layer 168 includes the same wavelength converting material
included in color converting layer 172 of sidewall 107. In this manner,
light emitted from LEDs located in preferential zone 1 is preferentially
directed to sidewall 107 and interior surface 166 for enhanced color
conversion. In some other embodiments, color converting layer 168
includes a different wavelength converting material than that included in
color converting layer 172.

[0074]FIG. 15 illustrates an example of a side emitting LED based
illumination module that preferentially directs light emitted from LEDs
102A and 102B toward sidewall 107 and preferentially directs light
emitted from LEDs 102C and 102D toward top wall 173. In side-emitting
embodiments, combined light 141 is emitted from LED based illumination
module through transmissive sidewall 107. In some embodiments, top wall
173 is reflective and is shaped to direct light toward sidewall 107.

[0075]FIG. 16 is illustrative of a cross-sectional, side view of an LED
based illumination module in one embodiment. As illustrated, LED based
illumination module includes a plurality of LEDs 102A-102D, a sidewall
107 and an output window 108. Sidewall 107 includes a reflective layer
171 and a color converting layer 172. Color converting layer 172 includes
a wavelength converting material (e.g., a red-emitting phosphor
material). Output window 108 includes a transmissive layer 134 and a
color converting layer 135. Color converting layer 135 includes a
wavelength converting material with a different color conversion property
than the wavelength converting material included in sidewall 107 (e.g., a
yellow-emitting phosphor material). LED based illumination module also
includes a transmissive element 190 disposed above LEDs 102A-102D. As
depicted transmissive element 190 is physically separated from the light
emitting surfaces of the LEDs 102. However, in some other embodiments,
transmissive element 190 is physically coupled to the light emitting
surfaces of the LEDs 102 by an optically transmissive medium (e.g.,
silicone, optical adhesive, etc.). As depicted, transmissive element 190
is a plate of optically transmissive material (e.g., glass, sapphire,
alumina, polycarbonate, and other plastics etc.). However, any other
shape may be contemplated. As depicted in FIG. 16, color conversion
cavity 160 is formed by the interior surfaces of the LED based
illumination module including the interior surface of sidewall 107, the
interior surface of output window 108, and transmissive element 190. As
such, LEDs 102 are physically separated from color conversion cavity 160.
By spacing the wavelength converting materials from LEDs 102, heat from
the LEDs 102 to the wavelength converting materials is decreased. As a
result, the wavelength converting materials are maintained at a lower
temperature during operation. This increases the reliability and color
maintenance of the LED based illumination device 100.

[0076] In some embodiments, color converting layers 172 and 135 are not
included in LED based illumination device 100. In these embodiments,
substantially all of color conversion is achieved by phosphors included
with transmissive element 190.

[0077] Transmissive element 190 includes a first surface area with a first
wavelength converting material 191 and a second surface area with a
second wavelength converting material 192. The wavelength converting
materials 191 and 192 may be disposed on transmissive element 190 or
embedded within transmissive element 190. Additional wavelength
converting materials may also be included as part of transmissive element
190. For example, additional surface areas of transmissive element 190
may include additional wavelength converting materials. In some examples,
different wavelength converting materials may be layered on transmissive
element 190. As depicted in FIG. 16, wavelength converting material 191
is a red emitting phosphor that is preferentially illuminated by LEDs
102A and 102B. In addition, wavelength converting material 192 is a
yellow emitting phosphor that is preferentially illuminated by LEDs 102C
and 102D.

[0078] The LEDs 102A-102D of LED based illumination module emit light
directly into color conversion cavity 160. Light is mixed and color
converted within color conversion cavity 160 and the resulting combined
light 141 is emitted by LED based illumination module. A different
current source supplies current to LEDs 102 in different preferential
zones. In the example depicted in FIG. 16, current source 182 supplies
current 185 to LEDs 102A and 102B located in preferential zone 1.
Similarly, current source 183 supplies current 184 to LEDs 102C and 102D
located in preferential zone 2. By separately controlling the current
supplied to LEDs located in different preferential zones, the correlated
color temperatures (CCT) of combined light 141 output by LED based
illumination module may be adjusted over a broad range of CCTs. In some
embodiments, the LEDs 102 of LED based illumination device emit light
with a peak emission wavelength within five nanometers of each other. For
example, LEDs 102A-D all emit blue light with a peak emission wavelength
within five nanometers of each other. In this manner, white light emitted
from LED based illumination device 100 is generated in large part by
wavelength converting materials. Thus, color control is based on the
arrangement of different wavelength converting materials to be
preferentially illuminated by different subsets of LEDs.

[0079]FIG. 17 illustrates a top view of the LED based illumination module
depicted in FIG. 16. FIG. 16 depicts a cross-sectional view of LED based
illumination device 100 along section line, B, depicted in FIG. 17. As
illustrated in FIG. 17, wavelength converting material 191 covers a
portion of transmissive element 190 and wavelength converting material
192 covers another portion of transmissive element 190. LEDs in zone 2
(including LEDs 102A and 102B) preferentially illuminate wavelength
converting material 191. Similarly, LEDs in zone 1 (including LEDs 102C
and 102D) preferentially illuminate wavelength converting material 192.
In some embodiments, more than fifty percent of the light output by LEDs
in zone 1 is directed to wavelength converting material 191, while more
than fifty percent of the light output by LEDS in zone 2 is directed to
wavelength converting material 192. In some other embodiments, more than
seventy five percent of the light output by LEDs in zone 1 is directed to
wavelength converting material 191, while more than seventy five percent
of the light output by LEDS in zone 2 is directed to wavelength
converting material 192. In some other embodiments, more than ninety
percent of the light output by LEDs in zone 1 is directed to wavelength
converting material 191, while more than ninety percent of the light
output by LEDS in zone 2 is directed to wavelength converting material
192.

[0080] In one embodiment, light emitted from LEDs located in preferential
zone 1 is directed to wavelength converting material 191 that includes a
mixture of red and yellow emitting phosphor materials. When current
source 182 supplies current 185 to LEDs in preferential zone 1, the light
output 141 is a light with a correlated color temperature (CCT) less than
7,500 Kelvin. In some other examples, the light output has a CCT less
than 5,000 Kelvin. In some embodiments, the light output has a color
point within a degree of departure Δxy of 0.010 from a target color
point in the CIE 1931 xy diagram created by the International Commission
on Illumination (CIE) in 1931. Thus, when current is supplied to LEDs in
preferential zone 1 and substantially no current is supplied to LEDs in
preferential zone 2, the combined light output 141 from LED based
illumination module is white light that meets a specific color point
target (e.g., within a degree of departure Δxy of 0.010 within
3,000 Kelvin on the Planckian locus). In some embodiments, the light
output has a color point within a degree of departure Δxy of 0.004
from a target color point in the CIE 1931 xy diagram. In this manner,
there is no need to tune multiple currents supplied to different LEDs of
LED based illumination device 100 to achieve a white light output that
meets the specified color point target.

[0081] Wavelength converting material 192 includes a red emitting phosphor
material. When current source 183 supplies current 184 to LEDs in
preferential zone 2, the light output has a relatively low CCT. In some
examples the light output has a CCT less than 2,200 Kelvin. In some other
examples, the light output has a CCT less than 2,000 Kelvin. In some
other examples, the light output has a CCT less than 1,800 Kelvin. Thus,
when current is supplied to LEDs in preferential zone 2 and substantially
no current is supplied to LEDs in preferential zone 1, the combined light
output 141 from LED based illumination module is a very warm colored
light. By adjusting the current 185 supplied to LEDs located in zone 1
relative to the current 184 supplied to LEDs located in zone 2, the
amount of white light relative to colored light included in combined
light 141 may be adjusted. Thus, control of currents 184 and 185 may be
used to tune the CCT of light emitted from LED based illumination module
from a relatively high CCT to a relatively low CCT. In some examples,
control of currents 184 and 185 may be used to tune the CCT of light
emitted from LED based illumination module from a white light of at least
2,700 Kelvin to a warm light below 1,800 Kelvin). In some other examples,
a warm light below 1,700 Kelvin is achieved.

[0082]FIG. 18 illustrates a top view of the LED based illumination module
in another embodiment. FIG. 19 depicts a cross-sectional view of LED
based illumination device 100 along section line, C, depicted in FIG. 18.
As illustrated in FIG. 18, wavelength converting material 191 covers a
portion of transmissive element 190 and is preferentially illuminated by
LEDs in zone 1. Wavelength converting material 192 covers another portion
of transmissive element 190 and is preferentially illuminated by LEDs in
zone 2. LEDs in zone 3 do not preferentially illuminate either of
wavelength converting materials 191 or 192. LEDs in zone 3,
preferentially illuminate wavelength converting materials present in
color converting layers 135 and 172. In this embodiment, color converting
layer 172 includes a red-emitting phosphor material and color converting
layer 135 includes a yellow emitting phosphor material. However, other
combinations of phosphor materials may be contemplated. In some other
embodiments, color converting layers 135 and 172 are not implemented. In
these embodiments, color conversion is performed by wavelength conversion
materials included on transmissive element 190, rather than sidewalls 107
or output window 108.

[0083]FIG. 20 illustrates a range of color points achievable by the LED
based illumination device 100 depicted in FIGS. 18 and 19. When a current
is supplied to LEDs in zone 3, light 141 emitted from LED based
illumination device 100 has a color point 231 illustrated in FIG. 20.
Light emitted from LED based illumination device 100 has a color point
within a degree of departure Oxy of 0.010 in the CIE 1931 xy diagram from
a target color point of less than 5,000 Kelvin on the Planckian locus
when current is supplied to LEDs in zone 3 and substantially no current
is supplied to LEDs in zones 1 and 2. When current source 183 supplies
current 184 to LEDs in preferential zone 1, the light emitted from LED
based illumination device 100 has a color point 232. Light emitted from
LED based illumination device 100 has a color point below the Planckian
locus in the CIE 1931 xy diagram with a CCT less than 1,800 Kelvin when
current is supplied to LEDs in zone 1 and substantially no current is
supplied to LEDs in zones 2 and 3. When current source 182 supplies
current 185 to LEDs in preferential zone 2, the light emitted from LED
based illumination device 100 has a color point 233. Light emitted from
LED based illumination device 100 has a color point above the Planckian
locus 230 in the CIE 1931 xy diagram 240 with a CCT less than 3,000
Kelvin when current is supplied to LEDs in zone 2 and substantially no
current is supplied to LEDs in zones 1 and 3.

[0084] By adjusting the currents supplied to LEDs located in zones 1, 2,
and 3, the light 141 emitted from LED based illumination module can be
tuned to any color point within a triangle connecting color points
231-233 illustrated in FIG. 20. In this manner, the light 141 emitted
from LED based illumination module can be tuned to achieve any CCT from a
relatively high CCT (e.g., approximately 3,000 Kelvin) to a relatively
low CCT (e.g., below 1,800 Kelvin).

[0085] As illustrated in FIG. 6, plotline 203 exhibits one achievable
relationship between CCT and relative flux for the embodiment illustrated
in FIGS. 18-19. As illustrated in FIG. 6, it is possible to reduce the
CCT of light emitted from LED based illumination device 100 from 3,000
Kelvin to approximately 2,200 Kelvin without a loss of flux. Further
reductions in CCT can be obtained from 2,200 Kelvin to approximately
1,750 Kelvin with an approximately linear reduction in relative flux from
100% to 55%. Relative flux can be further reduced without a change in CCT
by reducing current supplied to LEDs of LED based illumination device
100. Plotline 203 is presented by way of example to illustrate that LED
based illumination device 100 may be configured to achieve relatively
large changes in CCT with relatively small changes in flux levels (e.g.,
as illustrated in line 203 from 55-100% relative flux) and also achieve
relatively large changes in flux level with relatively small changes in
CCT (e.g., as illustrated in line 203 from 0-55% relative flux). However,
many other dimming characteristics may be achieved by reconfiguring both
the relative and absolute currents supplied to LEDs in different
preferential zones.

[0086] The aforementioned embodiment is provided by way of example. Many
other combinations of different zones of independently controlled LEDs
preferentially illuminating different color converting surfaces may be
contemplated to a desired dimming characteristic.

[0087] In some embodiments, components of color conversion cavity 160
including angled mounting pad 161 may be constructed from or include a
PTFE material. In some examples the component may include a PTFE layer
backed by a reflective layer such as a polished metallic layer. The PTFE
material may be formed from sintered PTFE particles. In some embodiments,
portions of any of the interior facing surfaces of color converting
cavity 160 may be constructed from a PTFE material. In some embodiments,
the PTFE material may be coated with a wavelength converting material. In
other embodiments, a wavelength converting material may be mixed with the
PTFE material.

[0088] In other embodiments, components of color conversion cavity 160 may
be constructed from or include a reflective, ceramic material, such as
ceramic material produced by CerFlex International (The Netherlands). In
some embodiments, portions of any of the interior facing surfaces of
color converting cavity 160 may be constructed from a ceramic material.
In some embodiments, the ceramic material may be coated with a wavelength
converting material.

[0089] In other embodiments, components of color conversion cavity 160 may
be constructed from or include a reflective, metallic material, such as
aluminum or Miro® produced by Alanod (Germany). In some embodiments,
portions of any of the interior facing surfaces of color converting
cavity 160 may be constructed from a reflective, metallic material. In
some embodiments, the reflective, metallic material may be coated with a
wavelength converting material.

[0090] In other embodiments, (components of color conversion cavity 160
may be constructed from or include a reflective, plastic material, such
as Vikuiti® ESR, as sold by 3M (USA), Lumirror® E60L manufactured
by Toray (Japan), or microcrystalline polyethylene terephthalate (MCPET)
such as that manufactured by Furukawa Electric Co. Ltd. (Japan). In some
embodiments, portions of any of the interior facing surfaces of color
converting cavity 160 may be constructed from a reflective, plastic
material. In some embodiments, the reflective, plastic material may be
coated with a wavelength converting material.

[0091] Cavity 160 may be filled with a non-solid material, such as air or
an inert gas, so that the LEDs 102 emits light into the non-solid
material. By way of example, the cavity may be hermetically sealed and
Argon gas used to fill the cavity. Alternatively, Nitrogen may be used.
In other embodiments, cavity 160 may be filled with a solid encapsulate
material. By way of example, silicone may be used to fill the cavity. In
some other embodiments, color converting cavity 160 may be filled with a
fluid to promote heat extraction from LEDs 102. In some embodiments,
wavelength converting material may be included in the fluid to achieve
color conversion throughout the volume of color converting cavity 160.

[0092] The PTFE material is less reflective than other materials that may
be used to construct or include in components of color conversion cavity
160 such as Miro® produced by Alanod. In one example, the blue light
output of an LED based illumination module constructed with uncoated
Miro® sidewall insert 107 was compared to the same module constructed
with an uncoated PTFE sidewall insert 107 constructed from sintered PTFE
material manufactured by Berghof (Germany). Blue light output from module
was decreased 7% by use of a PTFE sidewall insert. Similarly, blue light
output from module was decreased 5% compared to uncoated Miro®
sidewall insert 107 by use of an uncoated PTFE sidewall insert 107
constructed from sintered PTFE material manufactured by W.L. Gore (USA).
Light extraction from the module is directly related to the reflectivity
inside the cavity 160, and thus, the inferior reflectivity of the PTFE
material, compared to other available reflective materials, would lead
away from using the PTFE material in the cavity 160. Nevertheless, the
inventors have determined that when the PTFE material is coated with
phosphor, the PTFE material unexpectedly produces an increase in luminous
output compared to other more reflective materials, such as Miro®,
with a similar phosphor coating. In another example, the white light
output of an illumination module targeting a correlated color temperature
(CCT) of 4,000 Kelvin constructed with phosphor coated Miro® sidewall
insert 107 was compared to the same module constructed with a phosphor
coated PTFE sidewall insert 107 constructed from sintered PTFE material
manufactured by Berghof (Germany). White light output from module was
increased 7% by use of a phosphor coated PTFE sidewall insert compared to
phosphor coated Miro®. Similarly, white light output from module was
increased 14% compared to phosphor coated Miro® sidewall insert 107
by use of a PTFE sidewall insert 107 constructed from sintered PTFE
material manufactured by W.L. Gore (USA). In another example, the white
light output of an illumination module targeting a correlated color
temperature (CCT) of 3,000 Kelvin constructed with phosphor coated
Miro® sidewall insert 107 was compared to the same module constructed
with a phosphor coated PTFE sidewall insert 107 constructed from sintered
PTFE material manufactured by Berghof (Germany). White light output from
module was increased 10% by use of a phosphor coated PTFE sidewall insert
compared to phosphor coated Miro®. Similarly, white light output from
module was increased 12% compared to phosphor coated Miro® sidewall
insert 107 by use of a PTFE sidewall insert 107 constructed from sintered
PTFE material manufactured by W.L. Gore (USA).

[0093] Thus, it has been discovered that, despite being less reflective,
it is desirable to construct phosphor covered portions of the light
mixing cavity 160 from a PTFE material. Moreover, the inventors have also
discovered that phosphor coated PTFE material has greater durability when
exposed to the heat from LEDs, e.g., in a light mixing cavity 160,
compared to other more reflective materials, such as Miro®, with a
similar phosphor coating.

[0094] Although certain specific embodiments are described above for
instructional purposes, the teachings of this patent document have
general applicability and are not limited to the specific embodiments
described above. For example, any component of color conversion cavity
160 may be patterned with phosphor. Both the pattern itself and the
phosphor composition may vary. In one embodiment, the illumination device
may include different types of phosphors that are located at different
areas of a light mixing cavity 160. For example, a red phosphor may be
located on either or both of the insert 107 and the bottom reflector
insert 106 and yellow and green phosphors may be located on the top or
bottom surfaces of the output window 108 or embedded within the output
window 108. In one embodiment, different types of phosphors, e.g., red
and green, may be located on different areas on the sidewalls 107. For
example, one type of phosphor may be patterned on the sidewall insert 107
at a first area, e.g., in stripes, spots, or other patterns, while
another type of phosphor is located on a different second area of the
insert 107. If desired, additional phosphors may be used and located in
different areas in the cavity 160. Additionally, if desired, only a
single type of wavelength converting material may be used and patterned
in the cavity 160, e.g., on the sidewalls. In another example, cavity
body 105 is used to clamp mounting board 104 directly to mounting base
101 without the use of mounting board retaining ring 103. In other
examples mounting base 101 and heat sink 120 may be a single component.
In another example, LED based illumination module 100 is depicted in
FIGS. 1-3 as a part of a luminaire 150. As illustrated in FIG. 3, the LED
based illumination module may be a part of a replacement lamp or retrofit
lamp. But, in another embodiment, LED based illumination module may be
shaped as a replacement lamp or retrofit lamp and be considered as such.
Accordingly, various modifications, adaptations, and combinations of
various features of the described embodiments can be practiced without
departing from the scope of the invention as set forth in the claims.

Patent applications by Gerard Harbers, Sunnyvale, CA US

Patent applications by Hong Luo, San Jose, CA US

Patent applications by Serge J.a. Bierhuizen, San Jose, CA US

Patent applications in class LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL

Patent applications in all subclasses LIGHT SOURCE OR LIGHT SOURCE SUPPORT AND LUMINESCENT MATERIAL